The present invention relates to a system for the conduction of fluids and includes two concentrically arranged tubes and more particularly, the invention relates to a concentric tube system of the type requiring thermal insulation of the content of the interior tube. The content of the inner one of the two tubes may be a low temperature fluid or it may be a cryogenic cable, and particularly the space between the inner and the outer tube is flown through in some fashion by a coolant having as a primary function the thermal isolation of the interior content of the inner tube from the environment.
German printed patent application No. 23 42 160 discloses a cryogenic cable wherein the conductor is encased in a tubular shield which in turn carries a helical conductor for liquid nitrogen. The nitrogen conduit is metallically secured to the shielding tube containing the conductor. This kind of an arrangement may as such be satisfactory but is disadvantaged by the fact that the metallic connection e.g. welding between the conductor containing tube and the helical conduit for nitrogen has to be established as a separate working step. Moreover, in a two conduit type system contained within the same cable assembly a heat exchange between them cannot be prevented. The shielding tube as disclosed in that patent is rather rigid so that the arrangement as a whole is very stiff which means that installation is quite cumbersome.